This invention relates generally to a method and apparatus for testing audio and video program material recorded on a magnetic recording medium, such as magnetic tape and the like.
More particularly, the present invention is directed to a method and apparatus for high speed, fully automatic detection of erasures and/or over-recordings of audio and video program material recorded on video cassettes.
The recording of program material on VHS or Beta formated video tape cassettes has become widespread in recent years and the rental of prerecorded video cassette programs has been recently introduced on the market.
When prerecorded video tape is used under library or rental conditions, it is desirable to inspect the tape after each use to verify that the original recording has not been altered by erasure, over-recording or if other defects exist in the program material.
Prior art testing and verification of magnetic recording media, such as magnetic tape, for the most part have dealt with the testing and evaluation of the magnetic recording media used in data processing applications. These prior art testing techniques have been directed toward certifying the condition of the magnetic recording medium so that subsequently recorded data will not be lost or that spurious signals such as background noise will not be erroneously read as data.
Typically such prior art techniques as disclosed by U.S. Pat. Nos. 3,755,731 and 3,474,331 involve first recording signals on the medium then reading the recorded data to detect any dropout or non-recording of the data. In addition, the noise characteristics or "background" of the recording medium is tested by subsequently neutralizing or erasing the recorded test data and then sensing the tape for the presence of spurious signals that may be erroneously read as data.
Additionally, prior art has been directed towards preventing the unauthorized duplication of prerecorded program material. U.S. Pat. No. 3,883,892 discloses that, as a protective measure against editing or cutting of the recording medium, a control signal may be recorded at the time the recording is made or at a later time with which it is possible to check the original recording sequence and identify a copy of such a recording in which part(s) of the original information had been modified.